JP2013503211A - Fiber reinforced polyurethane molded product with three-dimensional raised structure - Google Patents

Abstract

  The present invention relates to a fiber-reinforced polyurethane molded article having a structural part such as a rib, a column or a dome, and this structural part is also fiber-reinforced.

Description

  The present invention relates to a fiber-reinforced polyurethane molded article having a structural part such as a rib, a column or a dome, and this structural part is also fiber-reinforced.

  Various polymer fiber reinforcements are widely used. By combining the fiber and the polymer matrix, a material having high specific rigidity and specific strength but low polymer density can be obtained. For this reason, such composite materials are of particular interest in lightweight construction applications. This composite material is mainly used to produce a two-dimensional structure in which the fibers can be evenly distributed.

  The use of fibers in polymer structures is known, for example, from US-A-3,824,201. The mat, non-woven fabric, long fiber or continuous fiber is wetted with the polyester-polyurethane composition described in the same patent publication and cut before it is cured.

  The use of glass fibers in addition to natural fibers for reinforced polymer moldings has also become established. For mechanical applications, glass fibers often take the form of rovings, nonwovens or wovens. Glass fiber has high strength and rigidity.

  The high strength of glass fiber is due to the influence of the sizing agent. The elongation at break of individual fibers can be up to 5%. The tensile and compressive strength of glass fiber provides the inherent rigidity of plastic materials while maintaining some flexibility.

  The elastic modulus of the glass fiber is almost the same as the elastic modulus of the glass solid mass. The glass fiber has an amorphous structure with random molecular orientation. Glass fiber has isotropic mechanical properties. Glass fiber exhibits ideal linear elasticity until it breaks. Glass fiber has very little material damping properties. In most cases, a significantly softer plastic material is used, so the stiffness of components made from glass fiber reinforced plastic material depends on the modulus of elasticity, the direction and volume fraction of the glass fiber, and to a lesser extent the matrix material It depends on the nature of the.

  Today, fiberglass reinforced plastic materials are used, for example, in aerospace engineering or in autopropulsion structures, including automobiles, transport machinery, construction machinery, trailer houses, farm equipment, trucks, semi-trailers, as well as stationary machinery or non-propelled Very important in housing parts for machines and truck boxes. In aerospace engineering, long fiber-containing composite materials are widely used in the manufacture of load-bearing parts. In the automotive industry, glass fibers or long fibers of natural fibers are currently used to reinforce thermoplastic parts (eg equipment).

  If long glass fibers are mixed into the polymer mixture, the long glass fibers are not arranged in a regular pattern, but rather randomly distributed. Long glass fibers randomly arranged in a polymer structure are known, for example, from US-A-4,791,019. However, methods for orienting glass fibers in a predetermined direction are also known. This is described, for example, in CN 101 314 931 A.

  Furthermore, a method for coating a two-dimensional element with a fiber reinforced polyurethane layer is also known. This coating increases the stability of the actual product. Such a method is described, for example, in WO 2007/075535 A2 and DE 10 2006 046 130 A1.

  Fiber-reinforced moldings are known from DE 196 149 56 A1 and DE 10 2006 022 846 A1. In addition to glass fibers, mats are also used to reinforce polymer structures. Such mats, woven fabrics or knitted fabrics may consist of glass fibers.

  When a fiber-reinforced polyurethane molded product is manufactured by a RIM (reaction injection molding) method, a mixture of polyurethane and fibers is usually two-dimensionally distributed to a lower mold of an open mold by a robot. The mixture is pressed into the desired shape by closing the mold with an upper mold or punch. The pressure releases the air bubbles trapped in the mixture. The shape of the product obtained depends on the shape of the mold. Glass fiber-derived structures may be present on the final product surface even after compression. In order to obtain a more uniform surface, glass fibers of various lengths can be used. For example, JP 59-086636 A describes glass fiber reinforced resin compositions in which the glass fibers have various lengths. WO 00/40650 also uses long and short fibers to reinforce polyurethane compositions. The short fiber has a length of 0.635 cm (1/4 inch) or less, and the long fiber has a length of 0.635 cm (1/4 inch) or more. PUR and long and short fibers are mixed at a fixed mass ratio. Thus, if long fibers do not enter the ribs, the total proportion of fibers in the ribs is always lower than the proportion in the two-dimensional region.

  DE 101 20 912 A1 describes composite parts made from polyurethane and their use in off-body parts. Corresponding composite parts consist of two layers, one layer comprising an entire short fiber reinforced polyurethane with a colorable surface finish. The second layer includes long fiber reinforced polyurethane. The use of short fibers results in a smooth or colorable surface. However, this layer has properties (particularly mechanical properties) other than those of the long fiber reinforced layer.

  A method for producing foamed parts is known from DE 10 2005 034 916 A1. Such foamed parts are for example made of fiber reinforced polyurethane. Support material is temporarily inserted into the structure. However, since the support material does not bond to the plastic material, the corresponding support material can be removed after curing. Then, in the obtained foamed part, a structural part appears on the surface.

  Such fiber reinforced polyurethanes are often produced by spraying. One such method is described, for example, in DE 10 2005 048 874 A1.

  The production of such materials is usually facilitated by compressed air, and the long fibers used for reinforcement are converted into a polyurethane reaction mixture spray jet by means of a funnel applicator fixed to a polyurethane (PUR) spray mixing head. It is implemented by introducing it laterally. Devices that produce polyurethane mixtures near the central tube are also commercially available. The long fibers are transported into the tube by air flow. At the end of the tube, a freshly mixed polyurethane component “liquid hose” wets the fiber / air stream. When reinforcing materials with long fibers, so-called rovings are often used as starting materials. Roving is a bundle of continuous stretched fibers without twisting. First, the roving is passed through a cutter attached to the PUR spray mixing head, and then the cut fibers are wetted with polyurethane.

  Such spraying methods often require as uniform a fiber-PUR reaction mixture distribution as possible across multiple layers. Therefore, in applications where high reproducibility is required, the robot guides the spray mixing head having a chute.

  The main advantage is that the long fibers are wetted with the polyurethane reaction mixture from essentially every aspect. Such PUR wet fibers do not have a single structure. Rather, air is mixed between the irregularly arranged long fibers. Therefore, PUR wet long fibers are introduced into an open mold for producing a molded product. The loosely stacked fibers are pushed into their final position by closing the mold while pressing, possibly at an elevated temperature. The mixed air is pushed out in this process. Using such a method, manufacturing various parts such as dashboard supports, door interiors, backrest equipment, hat racks, horizontal and vertical exteriors such as hoods, roof modules, side equipment Can do.

  For reinforcement, corresponding parts often include ribs, struts, domes or similar three-dimensional raised structures. These are required for later installation, bolting and insertion, for example. Such a structure is obtained from a groove and / or a conical recess in the upper die or punch. Often the gap width or diameter / cross-sectional area of this recess is so small that long fibers cannot enter the cavity with the foamable PUR. Only long fibers whose orientation matches the cavity can enter the cavity together with the foam. However, since most of the long fibers are inclined, the PUR mainly enters and the fibers do not enter at all or only slightly. Therefore, it cannot be ensured that the ribs, struts and / or domes that will be formed later are fiber reinforced.

  Such a structure containing no fibers or only a small percentage of fibers will have properties other than those of the molded body. For example, the longer the coefficient of long-term thermal expansion, the greater the number of fibers present. Due to the difference in the long-term thermal expansion coefficient, the actual molded product is bent when a heat load is applied.

  In addition, the protruding structure has a low flexural modulus. Thus, the dome, ribs and / or struts are not fully reinforced. Thus, using them as force transmission points can only hold loads that are less than is possible for fully fiber reinforced polyurethane moldings. Any insertion screw will not grip.

  The following describes a simple model for estimating the probability that fibers (eg, glass fibers) applied to a molded article by the spray method can enter an elongated part structure (eg, ribs).

Here we assume the following:
Each individual fiber is slender and hard (fiber length >> fiber thickness);
The fibers are first deposited on the mold plane and then transported together with the rising matrix material (viewed two-dimensionally) to a region perpendicular to the mold plane (eg rib);
• Fiber orientation and fiber length are used exclusively as criteria for whether the fiber can penetrate the ribs. Therefore, the probability of invasion by the fiber existing directly under the corresponding component structure (for example, rib) is estimated. Mutual interference between fibers is excluded for simplicity.
The fiber can enter the rib only if and only if the fiber length protruding in the rib width is less than twice the rib width (see FIG. 1).
-Regarding the distribution of fiber orientation (fiber angle), the probability of total orientation is equal, that is, there is no preferential orientation of fiber orientation.

［式中、Ｐは確率（０〜１の値）、ｇは好ましい事象数、ｍは起こり得る事象数である］。 The probability of occurrence of an event (here, application of fibers in a specific range of angles 0 <α _fiber <α _limit ) is defined as follows:

[Where P is the probability (value between 0 and 1), g is the number of events preferred, and m is the number of events that can occur].

である。 The number of possible events m corresponds to the number of all applied fibers. Preferred events are all of the fiber orientations between 0 ° and the α _limit , ie

It is.

In this way, the following is obtained as the probability of orientation of the fiber within the above angle range:

［式中、

である］。 However, in a complete 360 ° rotation of the fiber, the preferred angular range for entering the rib appears not only once but four times. The angular ranges are (0 <α _fiber <α _limit ), (180 ° −α _limit <α _fiber <180 °), (180 ° <α _fiber <180 ° + α _limit ) and (360 ° −α _limit <α _Fiber <360 °). Thus, the probability of fibers entering the rib (P _R ) is obtained as follows:

[Where:

Is].

If the ratio is greater than 0.5 relative to the fiber length of the rib width, since the fiber orientation is no longer critical, P _R becomes 1 by definition (see assumptions).

FIG. 2 shows the probability of fibers entering the ribs (P _R ) as a function of fiber length for four different rib widths.

FIG. 1 shows the relationship between fiber orientation, length and rib width. Assume that fibers whose length is at most twice the rib width can always enter the ribs (regardless of fiber angle). This is based on the idea that the fiber is in contact with only one rib edge and the limit aspect that can be dragged (tilted) into the rib is when the contact point between the fiber and the rib edge is in the center of the fiber. Based. Longer fibers can only enter the rib if the angle α _fiber is less than the limit angle α _limit . This is because otherwise the fibers are on both edges of the rib. If the fiber is on only one rib edge and the center of the fiber is on the outside of the rib, it is considered that such fiber cannot penetrate the rib. This assumption increases the probability of fibers entering the ribs. This is because the fibers reliably interfere with each other and in practice can hardly move.

US-A-3,824,201 US-A-4,791,019 CN 101 314 931 A WO 2007/0757535 A2 DE 10 2006 046 130 A1 DE 196 149 56 A1 DE 10 2006 022 846 A1 JP 59-086636 A WO 00/40650 DE 101 20 912 A1 DE 10 2005 034 916 A1 DE 10 2005 048 874 A1

  Accordingly, an object of the present invention is to provide a fiber-reinforced polyurethane molded article having a three-dimensional raised structure portion, in which both the molded article body and the structural portion are reinforced with fibers.

  In a first aspect, this object is a long fiber reinforced polyurethane molded article with a three-dimensional raised structure, in particular ribs, struts and / or domes, characterized in that it also contains short fibers in addition to long fibers. The weight ratio of short fibers and / or plate filler to fiber-free polyurethane matrix in the volume of ribs, struts and / or domes is short fibers and / or plates in a two-dimensional region other than the raised structure Achieved by polyurethane moldings greater than the weight ratio of filler to fiber-free polyurethane matrix.

FIG. 1 shows the relationship between fiber orientation, length and rib width. FIG. 2 shows the probability of fibers entering the ribs (P _R ) as a function of fiber length for four different rib widths. FIG. 3 shows the introduction of a mixture of polyurethane reaction mixture and long fibers into an open mold, the polyurethane is applied together with the short fibers locally to the corresponding part of the raised structure, and when the mold is closed, the short fiber containing polyurethane reaction Fig. 4 shows the process of free flowing of the mixture into the cavity. FIG. 4 shows a corresponding process in which short fibers or plate-like fillers are not used and the raised areas remain unfilled.

  Natural fibers or synthetic fibers can be used as long fibers. In addition to glass fibers and basalt fibers, carbon fibers, aramid fibers, natural fibers such as hemp fibers (sisal, flax) can also be used. It is preferable to use glass fibers.

  The long fibers are preferably derived from roving and cut with a correspondingly supplied cutter, so that the fibers in the molded product have a length of, for example, 1 to 30 cm, preferably 2.5 to 10 cm.

  According to the invention, the three-dimensional raised structure, i.e. the ribs, struts and / or dome, contains short fiber reinforced polyurethane. According to the invention, the term “short fibers” includes plate-like fillers such as layered silicates, in particular mica. Natural fibers or synthetic fibers are used as short fibers. The short fibers can be, for example, milled glass fibers, basalt fibers or carbon fibers. However, for example, wollastonite available under the trade name Tremin® or similar minerals may be used. According to the present invention, Tremin®, which is a needle-like crystal, is preferred.

  The dimension of the short fiber / plate-like filler is defined by its length / diameter. In particular, the length of the short fibers / diameter of the plate-like filler is 1 μm to 800 μm, preferably 4 μm to 600 μm, more preferably 100 μm to 500 μm.

  In accordance with the present invention, as shown in FIG. 3, a mixture of polyurethane reaction mixture and long fibers is introduced into an open mold. The polyurethane is then applied locally along with the short fibers to the corresponding location of the raised structure. When the short fiber-containing polyurethane reaction mixture is applied to these locations where cavities for ribs, struts and / or domes, especially in the punch, are located and the mold is closed, the short fiber-containing polyurethane reaction mixture is free to enter the cavity. Inflow.

  If cavities for ribs, struts and / or domes are present in the lower mold of the mold, the short fiber containing polyurethane reaction mixture is first applied to the cavity and then the long fiber containing polyurethane reaction mixture is applied two-dimensionally. can do.

  For example, the short fibers have a length short enough to freely flow into the cavities for ribs, struts and / or domes. For example, the short fibers flow into the cavity together with a PUR that may optionally foam. On the other hand, the long fibers are inclined and cannot enter the cavity together with the PUR, or it is difficult to enter.

  FIG. 4 describes the corresponding process in which no short fibers or plate-like fillers are used and the raised areas remain unfilled.

  Preferably, the polyurethane molded article of the present invention has an additional outer surface layer bonded to the surface where no three-dimensional structure exists. In particular, such outer skin layers are deep drawn sheets, especially acrylonitrile-butadiene-styrene (ABS), poly (methyl methacrylate) (PMMA), acrylonitrile-styrene-acrylate (ASA), polycarbonate (PC). And a deep-drawn molded sheet made of thermoplastic polyurethane, polypropylene (PP), polyethylene (PE) and / or polyvinyl chloride (PVC).

  The molded article may include a so-called in-mold coating or gel coat instead of the outer skin layer. In-mold coating is a method in which a plastic molded product is already painted in a mold. For example, a highly reactive two-component paint is applied to the mold by a suitable coating technique. Thereafter, in accordance with the present invention, the long fiber reinforced polyurethane layer is applied to the open mold. Subsequently, the short fiber reinforced polyurethane component is applied topically as described above and the mold is closed.

  In another aspect, the object of the present invention is achieved by a method for producing a fiber reinforced polyurethane molded article. Such methods include wetting the long glass fibers with the polyurethane reaction mixture, introducing the mixture into an open mold, applying the short fiber reinforced PUR locally, and closing the mold.

  Particularly preferred is a method in which the solid-containing gas stream is introduced into the mixing chamber at the head of the mixing head without metering into the already sprayed reaction mixture spray jet, but into a jet that is still liquid and not yet sprayed.

  In the context of the present invention, the “liquid jet of the PUR reaction mixture” means, inter alia, in a liquid state that is not yet present as a fine droplet state of the reaction mixture sprayed into the gas stream, ie in a particularly viscous liquid phase. Means a fluid jet of PUR material in the mixing chamber region for mixing the reaction components.

  Prior art methods essentially use a gas stream, or a corresponding nozzle to atomize the PUR reaction mixture, and meter the solid-containing gas stream into such an atomized PUR spray jet. For any spray jet, in this case, the distance between adjacent spray particles perpendicular to the main spray direction of the spray jet is considered to increase as the distance from the spray nozzle increases. The probability that solid particles collide with polyurethane droplets or filler particles that have already been wetted and thereby become wet will inevitably decrease rapidly. This situation changes if the mixing of filler and polyurethane is carried out in a mixing chamber according to the method of the invention.

  The device is characterized by introducing solids into the mixing chamber by means of a carrier gas stream, which impinges on the liquid jet of the PUR reaction mixture. The solid-containing gas flow can collide in the mixing chamber by being introduced into the mixing chamber from two or more points. Adjacent spray jets can form a large angle with each other and can be perpendicular to the circumference of the cylindrical mixing chamber. Therefore, they collide at the virtual center of gravity axis of the mixing chamber. However, they can also be introduced tangentially and may form vortices that define a circle perpendicular to the main direction of flow in the mixing chamber. In the method of the present invention, the particles cannot dissipate from one another or leave one another. This is because the mixing chamber walls hinder it. Thus, the solid is forced to wet with the PUR reaction mixture without loss in the mixing chamber in the process of the present invention and becomes part of a uniform gas / solid / PUR material mixture.

  It is preferred to further improve the quality of mixing of the resulting gas / solid / PUR material mixture in the mixing chamber with additional air vortices. Air vortices are generated by air from tangential air nozzles. The circular region surrounded by the air vortex is perpendicular to the main flow axis in the mixing chamber.

  According to the present invention, one and the same PUR may be used to use short fibers or to increase the proportion of short fibers. In normal methods, short fibers are added to the polyol formulation, so the proportion of short fibers does not change throughout the manufacturing process.

  The upper mold has a cavity into which the foamable PUR reaction mixture can later enter. In particular, the short fiber reinforced reaction mixture enters this cavity.

  The polyurethane molded product produced by the method of the present invention has not only high stability in an actual body. As the short fiber reinforced polyurethane component foams and fills the upper mold cavity, the subsequent dome, ribs and / or struts are also fiber reinforced. Thereby, a high stability of these structural parts is achieved.

List of reference signs 1 Newly mixed polyurethane 2 Long fiber 3 Upper mold 4 Recess for rib 5 Lower mold 6 Newly mixed short fiber-containing polyurethane 7 Configuration containing long glass fiber that has been two-dimensionally pressed Element 8 Rib made of component filled with unreinforced polyurethane 9 Rib made of component filled with short fiber reinforced polyurethane

Claims (16)

  A long-fiber reinforced polyurethane molded article having a three-dimensional raised structure, in particular ribs, struts and / or domes, characterized in that it also contains short fibers in addition to long fibres, comprising ribs, struts and / or domes The weight ratio of short fibers and / or plate filler to fiber-free polyurethane matrix in volume is the weight of short fibers and / or plate filler to fiber-free polyurethane matrix in the two-dimensional region other than the raised structure. A polyurethane molded product that is larger than the ratio.   The polyurethane molded article according to claim 1, wherein the long fibers include glass fibers.   2. The polyurethane molded product according to claim 1, characterized in that the long fibers have a length of 1 to 30 cm, in particular 2.5 to 10 cm.   2. The polyurethane molded article according to claim 1, characterized in that the short fibers have a length / diameter of 1 to 800 [mu] m, in particular 4 to 600 [mu] m.   The polyurethane molded product according to claim 4, wherein the short fibers include milled glass fibers.   The polyurethane molded product according to claim 5, wherein the short fibers include wollastonite fibers.   The polyurethane molded article according to any one of claims 1 to 6, wherein the long fiber reinforced surface further comprises an outer skin layer.   The outer skin layer is a deep-drawn molded sheet, in particular, acrylonitrile-butadiene-styrene (ABS), poly (methyl methacrylate) (PMMA), acrylonitrile-styrene-acrylate (ASA), polycarbonate (PC), thermoplastic polyurethane, The polyurethane molded article according to claim 7, comprising a deep-drawn molded sheet made of polypropylene (PP), polyethylene (PE) and / or polyvinyl chloride (PVC).   The polyurethane molded article according to claim 7, wherein the outer skin layer includes a two-layer sheet.   8. A polyurethane molded article according to claim 7, characterized in that the outer skin layer comprises a metal foil, in particular an aluminum foil or a steel foil.   The polyurethane molded product according to claim 7, wherein the outer skin layer includes an in-mold coating or a gel coat. (A) wetting the long fibers with the PUR reaction mixture and then introducing into the open mold;
The polyurethane molded article according to any one of claims 1 to 11, characterized by (b) a step of locally applying a short fiber reinforced PUR reaction mixture, and (c) a step of subsequently closing the mold with an upper mold. Manufacturing method.   13. A method according to claim 12, characterized in that steps (a) and (b) are interchanged. i) introducing a short fiber-containing gas stream into the polyurethane reaction mixture liquid jet and spraying the short fiber-containing polyurethane jet;
ii) optionally introducing a long fiber containing gas stream into this spray jet;
iii) spraying a PUR spray jet containing short fibers and optionally long fibers in an open mold or on a substrate support;
The method according to claim 12 or 13, wherein the amount of short fibers in i) is optionally increased if iv) the long fiber-containing gas stream is not introduced simultaneously.   15. A method according to any of claims 12 to 14, characterized in that an upper or lower mold with cavities for ribs, struts and / or domes is used.   First, the outer skin layer is placed in an open mold, then the PUR wet long fibers are introduced, on which the short fiber reinforced PUR reaction mixture is additionally applied topically, followed by the upper 16. A method according to any one of claims 12 to 15, characterized in that it is closed with a mold.

Images